An OLED converts electrical energy into light through a phenomenon called electroluminescence. To produce electroluminescence, the OLED is forward biased with an external voltage causing electrons and holes to be injected into an organic (carbon-based) material of the OLED. The electrons and holes combine in the organic material into an electron-hole pair and, in the process, emit a photon of light.
FIG. 1 shows an example OLED 100 formed on a substrate 102, such as glass. OLED 100 includes an anode 104, a cathode 106, and two or more layers of organic material 108. When a voltage source 110 with sufficient potential is applied as shown in FIG. 1, OLED 100 becomes forward biased and a current flows from cathode 106 to anode 104. Cathode 106 provides electrons to organic material 108, and anode 104 removes electrons from organic material 108 or, equivalently, gives holes to organic material 108. The electrons and holes combine in organic material 108 and emit photons of light through the phenomenon of electroluminescence. In general, as the current flowing from cathode 106 to anode 104 is increased, more electrons and holes are injected into organic material 108 and more photons of light are emitted thereby increasing the brightness or luminance of OLED 100. The color of the light emitted by OLED 100 depends on the type of organic molecules in organic material 108.
An array of OLEDs, such as OLED 100, can be deposited and patterned on a substrate to form a display. The brightness or luminance of each OLED in the array can be individually controlled to form an image viewable on the display. Today, such OLED display technology is used in a wide range of electronic devices and appliances, from small handheld mobile phones all the way up to large-panel TVs. The power consumption associated with OLED displays, although often superior to liquid crystal displays, can be relatively high because they are often driven with sufficient power to provide enough light output to compete with the strongest ambient light environments that they may be operated within, such as outdoor environments where sunlight can be strong.
One solution used to combat the issue of high power consumption is the inclusion and positioning of an ambient light sensor on the outer surface of an OLED display. The ambient light sensor is used to estimate the ambient light conditions of the environment where the OLED display is currently operating, which is then used to adjust the brightness of the OLEDs in the display to meet, but not greatly exceed, the brightness required for the ambient light conditions. Although this solution can improve power consumption, the addition of an ambient light sensor adds cost to the display and increases its overall size. In addition, for mobile devices such as smart phones or tablets, the ambient light sensor is prone to being obstructed by a user's hand or finger, or by a portion of the mobile device protective cover, making the ambient light sensor useless.
Therefore, what is needed is a method and apparatus for estimating ambient light conditions for an OLED display, while at the same time eliminating the need for a traditional ambient light sensor and the drawbacks associated therewith.
The embodiments of the present disclosure will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.